Movement disorders are neurological conditions that affect the ability to produce and control body movement. In particular, such disorders interfere with the speed, fluency, quality, and ease of movement. And, in some cases, cognitive and autonomic functions can be affected. Currently it is estimated that over 40 million individuals suffer from some sort of movement disorders. They can occur in all age groups from infancy to the elderly.
Treatment for movement disorders depends on the underlying cause. In most cases, the goal of treatment is to relieve symptoms. Treatment may include medication, botulinum toxin injection therapy, and surgery. Medications that are typically used include the following: antiepileptics, antiseizure medications, beta-blockers, dopamine agonists, and tranquilizers. However, these medications have a variety of side effects. Side effects of antiepileptics include dizziness, drowsiness, nausea, and vomiting. Antiseizure medications may cause a lack of coordination and balance (ataxia), dizziness, nausea, and fatigue. Side effects caused by beta-blockers include slowed heart rate (bradycardia), depression, light-headedness, and nausea. Dopamine agonists may cause nausea, headache, dizziness, and fatigue. Tranquilizers such as benzodiazepines may cause blood clots (thrombosis), drowsiness, and fatigue.
Botulinum toxin injection therapy is used to treat some types of movement disorders (e.g., spasmodic torticollis, blepharospasm, myoclonus, tremor). In this treatment, a potent neurotoxin (produced by the bacterium Clostridium botulinum) is injected into a muscle to inhibit the release of neurotransmitters that cause muscle contraction. In some cases, treatment is repeated every 3 to 4 months. However, patients may develop antibodies to the toxin over time, causing treatment to become ineffective. Side effects include temporary weakness in the group of muscles being treated, unintentional paralysis of muscles other than those being treated and rarely, flu-like symptoms.
When medication is ineffective, severe movement disorders may require surgery. In such instances, deep brain stimulation may be performed wherein a surgically implanted neurostimulator is used to deliver electrical stimulation to areas of the brain that control movement. The electrical charge blocks nerve signals that trigger abnormal movement. In deep brain stimulation, a lead is inserted through a small incision in the skull and is implanted in the targeted area of the brain. An insulated wire is then passed under the skin in the head, neck, and shoulder, connecting the lead to the neurostimulator, which is surgically implanted in the chest or upper abdomen. However, negative side effects of deep brain stimulation can occur, including: bleeding at the implantation site, depression, impaired muscle tone, infection, loss of balance, slight paralysis (paresis), slurred speech (dysarthia), and tingling (parethesia) in the head or the hands.
Another type of surgical treatment for motion disorders is ablative surgery. Ablative surgery locates, targets, and then destroys (ablates) a defined area of the brain that produces chemical or electrical impulses that cause abnormal movements. In this surgery, a heated probe or electrode is inserted into the targeted area. The patient remains awake during the procedure to determine if the problem has been eliminated. A local anesthetic is used to dull the outer part of the brain and skull. The brain is insensitive to pain, so the patient does not feel the actual procedure. However, in some cases, it may be difficult to estimate how much tissue to destroy and the amount of heat to use. This type of surgery involves either ablation in the part of the brain called the globus pallidus (called pallidotomy) or ablation of brain tissue in the thalamus (called thalamotomy). Pallidotomy may be used to eliminate uncontrolled dyskinesia (e.g., jerky, involuntary movements) and thalamotomy may be performed to eliminate tremor. A related procedure, cryothalamotomy, uses a supercooled probe that is inserted into the thalamus to freeze and destroy areas that produce tremors.
Aside from the risks and side effects associated with the above described therapies, such treatments are not always effective in treating the movement disorder. Therefore, improved therapies with higher effectiveness and lower side effects are desired. At least some of these objectives will be met by the following invention.